We present the unambiguous discovery of six new class II methanol maser transitions , three of which are torsionally excited ( v _ { t } =1 ) .
The newly discovered 6.18-GHz 17 _ { − 2 } \rightarrow 18 _ { − 3 } E ( v _ { t } =1 ) , 7.68-GHz 12 _ { 4 } \rightarrow 13 _ { 3 } A ^ { - } ( v _ { t } =0 ) , 7.83-GHz 12 _ { 4 } \rightarrow 13 _ { 3 } A ^ { + } ( v _ { t } = 0 ) , 20.9-GHz 10 _ { 1 } \rightarrow 11 _ { 2 } A ^ { + } ( v _ { t } =1 ) , 44.9-GHz 2 _ { 0 } \rightarrow 3 _ { 1 } E ( v _ { t } =1 ) and 45.8-GHz 9 _ { 3 } \rightarrow 10 _ { 2 } E ( v _ { t } =0 ) methanol masers were detected towards G 358.931 - 0.030 , where the known 6.68-GHz maser has recently been reported to be undergoing a period flaring .
The detection of the v _ { t } =1 torsionally excited lines corroborates one of the missing puzzle pieces in class II maser pumping , but the intensity of the detected emission provides an additional challenge , especially in the case of the very highly excited 6.18-GHz line .
Together with the newly detected v _ { t } = 0 lines , these observations provide significant new information which can be utilised to improve class II methanol maser modelling .
We additionally present detections of 6.68- , 19.9- , 23.1- and 37.7-GHz class II masers , as well as 36.2- and 44.1-GHz class I methanol masers , and provide upper limits for the 38.3- and 38.5-GHz class II lines .
Near simultaneous Australia Telescope Compact Array ( ATCA ) observations confirm that all 10 of the class II methanol maser detections are co-spatial to \sim 0.2 arcsec , which is within the uncertainty of the observations .
We find significant levels of linearly polarised emission in the 6.18- , 6.67- , 7.68- , 7.83- , 20.9- , 37.7- , 44.9- and 45.8-GHz transitions , and low levels of circular polarisation in the 6.68- , 37.7- and 45.8-GHz transitions .